3a-Energetics

Question 1

Question: What is an exothermic reaction?

Answer 1

An exothermic reaction releases energy to the surroundings, usually as heat, causing a temperature increase. Example: Combustion of fuels.

Question 2

Question: What is an endothermic reaction?

Answer 2

An endothermic reaction absorbs energy from the surroundings, causing a temperature decrease. Example: Thermal decomposition of calcium carbonate.

Question 3

Question: How can you identify an exothermic or endothermic reaction?

Answer 3

Answer: Measure the temperature change of the surroundings using a thermometer. If the temperature increases, the reaction is exothermic; if it decreases, the reaction is endothermic.

Question 4

Question: What is enthalpy change (ΔH)?

Answer 4

Answer: Enthalpy change is the heat energy change in a reaction at constant pressure. It is negative for exothermic reactions and positive for endothermic reactions.

Question 5

Question: What is activation energy?

Answer 5

Answer: Activation energy is the minimum amount of energy needed for a reaction to occur by breaking bonds in reactants.

Question 6

Question: How do bond breaking and bond making relate to energy changes?

Answer 6

Answer:

Bond breaking absorbs energy (endothermic).

Bond making releases energy (exothermic).

If more energy is released than absorbed, the reaction is exothermic.

If more energy is absorbed than released, the reaction is endothe

Question 7

Question: How do you calculate enthalpy change using bond energies?

Answer 7

Answer:ΔH = Total energy needed to break bonds - Total energy released in making bonds

Question 8

Question: What are examples of exothermic and endothermic reactions?

Answer 8

Answer:

Exothermic: Combustion, neutralization, respiration.

Endothermic: Photosynthesis, thermal decomposition, dissolving certain salts in water.

Question 9

Practical: Investigating Temperature Changes in Reactions

Method:

Answer 9

Mix reactants in a polystyrene cup with a thermometer.

Measure the temperature change before and after the reaction.

Question 10

Practical: Investigating Temperature Changes in Reactions
Results & conclution

Answer 10

Results:

If the temperature increases, the reaction is exothermic.

If the temperature decreases, the reaction is endothermic.

Conclusion:

The energy change depends on whether the reaction releases or absorbs heat.